A new coin cell battery is the first thing to try. It's a cheap possible fix. Buy the battery anywhere that sells batteries. Directions are in your manual. Support for OptiPlex 3070 | Documentation | Dell US

Meanwhile, I kept searching.  The 5 white and 2 amber pattern indicates:  BIOS Post code (Old LED pattern 0001) Corrupt BIOS.

How to Recover the BIOS on a Dell Computer or Tablet  Includes video.

This article is a little newer and includes the Optiplex 3070:  BIOS Recovery Steps for a No Post issue on OptiPlex, Alienware, XPS, Vostro ,Inspiron Desktop and Inspiron AIO PCs 

@Mary G - @hinetsuez indicated already replacing battery and doing a BIOS reset.

@hinetsuez,

I couldn't find that code in any Dell diagnostic documentation.  Meanwhile, there's a couple of troubleshooting guides that may help:  https://www.dell.com/support/home/en-us/product-support/product/optiplex-3070-desktop/docs 

Check if all psu cables are connected well but be caution.. any wrong may burn pc parts and disconnect the power from plug befor doing that. After finishing try to turn on the pc.

May be your problem due to a problem in usb connectors

i try new battry and the problem as sam no changed

The Ram that comes with the PC is of worst quality. I got the same problem with the Ram chip in both PCs. Replace the Ram.

What RAM did your Dell come with, Hynix?  I had to replace Hynix a few years ago.